Canister fluid level detection in reduced pressure therapy systems

ABSTRACT

Embodiments of negative pressure wound therapy apparatuses and methods for using such apparatuses are disclosed. In some embodiments, a negative pressure wound therapy apparatus includes a controller configured to determine a level of exudate in a canister (or a dressing) based at least in part on one or more characteristics of pressure signals generated by a negative pressure source and monitored by a pressure sensor. One such characteristic of the pressure signals can be amplitude, which may increase as a level of exudate in the canister (or dressing) increases. The canister (or dressing) can include a filter configured to become occluded in order to prevent overflow of the canister (or dressing). The controller can be additionally configured to detect and indicate a canister (or dressing) pre-full condition before the filter becomes occluded. More efficient and reliable operation of the negative pressure wound therapy apparatus can thereby be attained.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/912,071, filed Feb. 12, 2016, which is a national stage applicationof International Patent Application No. PCT/US2014/050233, filed Aug. 7,2014, which claims the benefit of U.S. Provisional Application No.61/865,516, filed on Aug. 13, 2013; disclosures of which are herebyincorporated by reference in their entireties.

BACKGROUND Field

Embodiments of the present disclosure relate to methods and apparatusesfor dressing and treating a wound with reduced pressure therapy ortopical negative pressure (TNP) therapy. In particular, but withoutlimitation, embodiments disclosed herein relate to negative pressuretherapy devices, methods for controlling the operation of TNP systems,and methods of using TNP systems.

Description of the Related Art

Embodiments of the present disclosure relate to methods and apparatusesfor dressing and treating a wound with reduced pressure therapy ortopical negative pressure (TNP) therapy. In particular, but withoutlimitation, embodiments disclosed herein relate to negative pressuretherapy devices, methods for controlling the operation of TNP systems,and method of using TNP systems. In addition, embodiments disclosedherein relate to attachment mechanisms or systems for negative pressuretherapy devices.

SUMMARY

In some embodiments, a negative pressure wound therapy apparatusincludes a negative pressure source configured to be in fluidcommunication with a wound dressing, the negative pressure sourceconfigured to provide negative pressure to the wound, a canisterconfigured to be in fluid communication with the dressing and thenegative pressure source, the canister configured to collect exudateremoved from the wound, and a pressure sensor configured to monitor oneor more characteristics of pressure signals generated by the negativepressure source. The apparatus also includes a controller configured todetermine a level of exudate in the canister based at least in part onthe measured one or more characteristics of the pressure signals.

The apparatus of the preceding paragraph may also include anycombination of the following features described in this paragraph, amongothers described herein. The measured one or more characteristics of thepressure signals can include magnitude of the pressure signals, and themagnitude of the pressure signals can increase as the level of exudatein the canister increases. The canister can include a filter configuredto become occluded in order to prevent overflow of the canister and thecontroller can be further configured to detect a canister pre-fullcondition before the filter becomes occluded. The controller can alsoprovide an indication of the canister pre-full condition to a user. Thecontroller can be configured to determine the level of exudate in thecanister based at least in part on the measured one or morecharacteristics of the pressure signals and a measured activity level ofthe negative pressure source. The negative pressure source can include avacuum pump and the activity level of the negative pressure sourcecorresponds to a speed of the vacuum pump. The apparatus can include atachometer configured to measure the speed of the vacuum pump.

The apparatus of any of the preceding paragraphs may also include anycombination of the following features described in this paragraph, amongothers described herein. The apparatus can include a fluid flow pathconfigured to fluidically connect the dressing, the canister, and thenegative pressure source, and the controller can be further configuredto determine a leak rate of fluid in the flow path based at least inpart on the activity level of the negative pressure source and determinethe level of exudate in the canister based at least in part on themeasured one or more characteristics of the pressure signals and thedetermined leak rate. The controller can be configured to remove noisefrom the measured one or more characteristics of the pressure signals.The controller can be configured to determine the level of exudate inthe canister based at least in part on comparing the measured one ormore characteristics of the pressure signals to one or more thresholds.The measured one or more characteristics can include magnitude andfrequency of pressure pulses and the controller can be configured todetermine the level of exudate in the canister based at least in part onthe magnitude and frequency of the pressure signals. The magnitude ofthe pressure signals can increase as the level of exudate in thecanister increases and the frequency of the pressure signals candecrease as the level of exudate in the canister increases.

The apparatus of any of the preceding paragraphs may also include anycombination of the following features described in this paragraph, amongothers described herein. The controller can be configured to determinethe level of exudate in the canister irrespective of an intensity of aleak present in a fluid flow path configured to fluidically connect thedressing, the canister, and the negative pressure source. The controllercan be configured to determine the level of exudate in the canisterbased at least in part on a change in the measured one or morecharacteristics of the pressure signals. The apparatus can include awound dressing configured to be placed over a wound.

In certain embodiments, a method of operating a negative pressure woundtherapy apparatus includes monitoring pressure signals generated by anegative pressure source in fluid communication with a wound dressingand a canister and determining a level of aspirated exudate in thecanister based at least in part on one or more characteristics of themonitored pressure signals.

The method of the preceding paragraph may also include any combinationof the following features described in this paragraph, among othersdescribed herein. One or more characteristics of the monitored pressuresignals can include magnitude of the pressure signals, and the magnitudeof the pressure signals can increase as the level of exudate in thecanister increases. The canister can include a filter configured tobecome occluded in order to prevent overflow of the canister and themethod can further include detecting a canister pre-full conditionbefore the filter becomes occluded. An indication of the canisterpre-full condition can be provided to a user. The method can includemeasuring activity level of the negative pressure source and determiningthe level of exudate in the canister based at least in part on the oneor more characteristics of the monitored pressure signals and themeasured activity level. The negative pressure source can include avacuum pump and the activity level of the negative pressure sourcecorresponds to a speed of the vacuum pump. A tachometer can used tomeasure the speed of the vacuum pump. The method can include determininga leak rate of fluid in a flow path based at least in part on theactivity level of the negative pressure source and determining the levelof exudate in the canister based at least in part on the one or morecharacteristics of the monitored pressure signals and the determinedleak rate. The fluid flow path can fluidically connect a dressing placedover a wound, the negative pressure source, and the canister.

The method of any of the preceding paragraphs may also include anycombination of the following features described in this paragraph, amongothers described herein. The method can include removing noise from thepressure signal measurements. The method can include determining thelevel of exudate in the canister based at least in part on comparing theone or more characteristics of the monitored pressure signals to one ormore thresholds. The one or more characteristics of the monitoredpressure signals can include magnitude and frequency of the pressuresignals and the method can further include determining the level ofexudate in the canister based at least in part on the magnitude and thefrequency of the monitored pressure signals. The magnitude of thepressure signals can increase as the level of exudate in the canisterincreases and the frequency of the pressure signals can decrease as thelevel of exudate in the canister increases. Determining the level ofaspirated exudate in the canister is performed irrespective of anintensity of a leak present in a fluid flow fluidically connecting thedressing, the canister, and the negative pressure source. The method caninclude determining the level of exudate in the canister based at leastin part on a change in the one or more characteristics of the monitoredpressure signals.

In various embodiments, a negative pressure wound therapy apparatusincludes a dressing configured to be placed over a wound, the dressingconfigured to collect exudate removed from the wound, a negativepressure source configured to be in fluid communication with thedressing, the negative pressure source configured to provide negativepressure to the wound, and a pressure sensor configured to monitor oneor more characteristics of pressure signals generated by the negativepressure source. The apparatus also includes a controller configured todetermine a level of exudate in the dressing based at least in part onthe monitored one or more characteristics of the pressure signals.

The apparatus of any of the preceding paragraphs may also include anycombination of the following features described in this paragraph, amongothers described herein. The monitored one or more characteristics ofthe pressure signals can include magnitude of the pressure signals, andthe magnitude of the pressure signals can increase as the level ofexudate in the dressing increases. The dressing can include a filterconfigured to become occluded in order to prevent overflow and thecontroller can be further configured to detect a dressing pre-fullcondition before the filter becomes occluded and provide an indicationof the dressing pre-full condition to a user. The controller can befurther configured to determine the level of exudate in the dressingbased at least in part on the monitored one or more characteristics ofthe pressure signals and a measured activity level of the negativepressure source. The apparatus can further include a fluid flow pathconfigured to fludicially connect the dressing and the negative pressuresource and the controller can be further configured to determine a leakrate of fluid in the flow path based at least in part on the activitylevel of the negative pressure source and to determine the level ofexudate in the dressing based at least in part on the monitored one ormore characteristics of the pressure signals and the determined leakrate.

The apparatus of any of the preceding paragraphs may also include anycombination of the following features described in this paragraph, amongothers described herein. The controller can be configured to determinethe level of exudate in the dressing based at least in part on comparingthe monitored one or more characteristics of the pressure signals to oneor more thresholds The monitored one or more characteristics of thepressure signals can include magnitude and frequency of the pressuresignals and the controller can be further configured to determine thelevel of exudate in the dressing based at least in part on the magnitudeand the frequency of the pressure signals. The magnitude of the pressuresignals can increase as the level of exudate in the dressing increasesand the frequency of the pressure signals can decrease as the level ofexudate in the dressing increases. The controller can be configured todetermine the level of exudate in the dressing irrespective of anintensity of a leak present in a fluid flow path configured tofluidically connect the dressing and negative pressure source. Thecontroller can be configured to determine the level of exudate in thedressing based at least in part on a change in the monitored one or morecharacteristics of the pressure signals.

In some embodiments, a method of operating a negative wound therapyapparatus includes monitoring pressure signals generated by a negativepressure source in fluid communication with a wound dressing and acanister and determining a level of aspirated exudate in the dressingbased at least in part on one or more characteristics of the monitoredpressure signals.

The method of any of the preceding paragraphs may also include anycombination of the following features described in this paragraph, amongothers described herein. The monitored one or more characteristics ofthe pressure signals include magnitude of the pressure signals, andwherein the magnitude of the pressure signals increases as the level ofexudate in the dressing increases. The dressing can include a filterconfigured to become occluded in order to prevent overflow and themethod can further include detecting a dressing pre-full conditionbefore the filter becomes occluded and providing an indication of thedressing pre-full condition to a use. The method can further includemeasuring activity level of the negative pressure source and determiningthe level of exudate in the dressing based at least in part on themonitored one or more characteristics of the pressure signals and themeasured activity level.

The method of any of the preceding paragraphs may also include anycombination of the following features described in this paragraph, amongothers described herein. The method can include determining a leak rateof fluid in the flow path based at least in part on the activity levelof the negative pressure source, the fluid flow path fludiciallyconnecting the dressing and the negative pressure source and determiningthe level of exudate in the dressing based at least in part on themonitored one or more characteristics of the pressure signals and thedetermined leak rate. The method can include determining the level ofexudate in the dressing based at least in part on comparing themonitored one or more characteristics of the pressure signals to one ormore thresholds. The monitored one or more characteristics of thepressure signals can include magnitude and frequency of the pressuresignals and the method can further include determining the level ofexudate in the dressing based at least in part on the magnitude and thefrequency of the pressure signals. The magnitude of the pressure signalscan increase as the level of exudate in the dressing increases and thefrequency of the pressure signals can decrease as the level of exudatein the dressing increases. The method can further include determiningthe level of exudate in the dressing irrespective of an intensity of aleak present in a fluid flow path fluidically connecting the dressingand negative pressure source.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described hereinafter,by way of example only, with reference to the accompanying drawings inwhich:

FIG. 1 illustrates a reduced pressure wound therapy system according tosome embodiments.

FIGS. 2A-2E illustrate a pump assembly and canister according to someembodiments.

FIG. 3 illustrates fluid flow paths according to some embodiments.

FIG. 4 illustrates a graph of pressure signals according to someembodiments.

FIGS. 5A-5D illustrate graphs of pressure signals according to someembodiments.

FIGS. 6A-6D illustrate graphs of pressure signals according to someembodiments.

FIGS. 7A-7D illustrate graphs of pressure signals according to someembodiments.

FIGS. 8A-8D illustrate graphs of pressure signals according to someembodiments.

FIG. 9 illustrates sensed pressure magnitude ripple according to someembodiments.

FIG. 10 illustrates a process of detecting proximal blockages accordingto some embodiments.

DETAILED DESCRIPTION

Overview

Embodiments disclosed herein relate to systems and methods of treating awound with reduced pressure. As is used herein, reduced or negativepressure levels, such as −X mmHg, represent pressure levels relative tonormal ambient atmospheric pressure, which can correspond to 760 mmHg(or 1 atm, 29.93 inHg, 101.325 kPa, 14.696 psi, etc.). Accordingly, anegative pressure value of −X mmHg reflects absolute pressure that is XmmHg below 760 mmHg or, in other words, an absolute pressure of (760−X)mmHg. In addition, negative pressure that is “less” or “smaller” than XmmHg corresponds to pressure that is closer to atmospheric pressure(e.g., −40 mmHg is less than −60 mmHg). Negative pressure that is “more”or “greater” than −X mmHg corresponds to pressure that is further fromatmospheric pressure (e.g., −80 mmHg is more than −60 mmHg). In someembodiments, local ambient atmospheric pressure is used as a referencepoint, and such local atmospheric pressure may not necessarily be, forexample, 760 mmHg.

Embodiments of the present invention are generally applicable to use intopical negative pressure (“TNP”) or reduced pressure therapy systems.Briefly, negative pressure wound therapy assists in the closure andhealing of many forms of “hard to heal” wounds by reducing tissueoedema, encouraging blood flow and granular tissue formation, and/orremoving excess exudate and can reduce bacterial load (and thusinfection risk). In addition, the therapy allows for less disturbance ofa wound leading to more rapid healing. TNP therapy systems can alsoassist in the healing of surgically closed wounds by removing fluid. Insome embodiments, TNP therapy helps to stabilize the tissue in theapposed position of closure. A further beneficial use of TNP therapy canbe found in grafts and flaps where removal of excess fluid is importantand close proximity of the graft to tissue is required in order toensure tissue viability.

In some embodiments, a negative pressure wound therapy apparatusincludes a dressing configured to be placed over a wound and a source ofnegative pressure configured to be in fluid communication with thedressing. The source of negative pressure is configured to providenegative pressure to the wound. The apparatus can also include acanister configured to collect exudate removed from the wound. Thecanister can be configured to be in fluid communication with thedressing and the negative pressure source. The apparatus also includes apressure sensor configured to monitor pressure signals generated by thenegative pressure source and a controller. The controller can beconfigured to determine a level of exudate in the canister (or in thedressing) based at least in part on one or more characteristics of themonitored pressure signals. The one or more characteristics of thepressure signals can change as a level of exudate in the canisterincreases.

In various embodiments, a method of operating a negative pressure woundtherapy apparatus includes monitoring pressure signals generated by anegative pressure source in fluid communication with a dressing and acanister. The method also includes determining a level of exudate in thecanister (or in the dressing) based at least in part on one or morecharacteristics of the monitored pressure signals. The one or morecharacteristics of the pressure signals can change as a level of exudatein the canister increases.

In some embodiments, systems and methods for determining an amount offlow restriction or reduced volume in front of a negative pressureutilize one or more characteristics of monitored pressure signals. Forexample, the magnitude of the pressure signals can increase asrestriction to flow increase, which effectively reduces the volume infront of a negative pressure source. The volume in front of the negativepressure source may decrease due to filling of a canister or dressingwith exudate removed from a wound.

Negative Pressure System

FIG. 1 illustrates an embodiment of a negative or reduced pressure woundtreatment (or TNP) system 100 comprising a wound filler 130 placedinside a wound cavity 110, the wound cavity sealed by a wound cover 120.The wound filler 130 in combination with the wound cover 120 can bereferred to as wound dressing. A single or multi lumen tube or conduit140 is connected the wound cover 120 with a pump assembly 150 configuredto supply reduced pressure. The wound cover 120 can be in fluidiccommunication with the wound cavity 110. In any of the systemembodiments disclosed herein, as in the embodiment illustrated in FIG.1, the pump assembly can be a canisterless pump assembly (meaning thatexudate is collected in the wound dressing is transferred via tube 140for collection to another location). However, any of the pump assemblyembodiments disclosed herein can be configured to include or support acanister. Additionally, in any of the system embodiments disclosedherein, any of the pump assembly embodiments can be mounted to orsupported by the dressing, or adjacent to the dressing. The wound filler130 can be any suitable type, such as hydrophilic or hydrophobic foam,gauze, inflatable bag, and so on. The wound filler 130 can beconformable to the wound cavity 110 such that it substantially fills thecavity at atmospheric pressure, and also may have a substantiallyreduced compressed volume when under negative pressure. The wound cover120 can provide a substantially fluid impermeable seal over the woundcavity 110. In some embodiments, the wound cover 120 has a top side anda bottom side, and the bottom side adhesively (or in any other suitablemanner) seals with wound cavity 110. The conduit 140 or any otherconduit disclosed herein can be formed from polyurethane, PVC, nylon,polyethylene, silicone, or any other suitable material.

Some embodiments of the wound cover 120 can have a port (not shown)configured to receive an end of the conduit 140. In some embodiments,the conduit 140 can otherwise pass through and/or under the wound cover120 to supply reduced pressure to the wound cavity 110 so as to maintaina desired level of reduced pressure in the wound cavity. The conduit 140can be any suitable article configured to provide at least asubstantially sealed fluid flow pathway between the pump assembly 150and the wound cover 120, so as to supply the reduced pressure providedby the pump assembly 150 to wound cavity 110.

The wound cover 120 and the wound filler 130 can be provided as a singlearticle or an integrated single unit. In some embodiments, no woundfiller is provided and the wound cover by itself may be considered thewound dressing. The wound dressing may then be connected, via theconduit 140, to a source of negative pressure, such as the pump assembly150. In some embodiments, though not required, the pump assembly 150 canbe miniaturized and portable, although larger conventional pumps suchcan also be used.

The wound cover 120 can be located over a wound site to be treated. Thewound cover 120 can form a substantially sealed cavity or enclosure overthe wound site. In some embodiments, the wound cover 120 can beconfigured to have a film having a high water vapour permeability toenable the evaporation of surplus fluid, and can have a superabsorbingmaterial contained therein to safely absorb wound exudate. It will beappreciated that throughout this specification reference is made to awound. In this sense it is to be understood that the term wound is to bebroadly construed and encompasses open and closed wounds in which skinis torn, cut or punctured or where trauma causes a contusion, or anyother surficial or other conditions or imperfections on the skin of apatient or otherwise that benefit from reduced pressure treatment. Awound is thus broadly defined as any damaged region of tissue wherefluid may or may not be produced. Examples of such wounds include, butare not limited to, acute wounds, chronic wounds, surgical incisions andother incisions, subacute and dehisced wounds, traumatic wounds, flapsand skin grafts, lacerations, abrasions, contusions, burns, diabeticulcers, pressure ulcers, stoma, surgical wounds, trauma and venousulcers or the like. In some embodiments, the components of the TNPsystem described herein can be particularly suited for incisional woundsthat exude a small amount of wound exudate.

Some embodiments of the system are designed to operate without the useof an exudate canister. Some embodiments can be configured to support anexudate canister. In some embodiments, configuring the pump assembly 150and tubing 140 so that the tubing 140 can be quickly and easily removedfrom the pump assembly 150 can facilitate or improve the process ofdressing or pump changes, if necessary. Any of the pump embodimentsdisclosed herein can be configured to have any suitable connectionbetween the tubing and the pump.

In some embodiments, the pump assembly 150 can be configured to delivernegative pressure at a desired negative pressure setpoint, which can beselected or programmed to be approximately −80 mmHg, or between about−20 mmHg and −200 mmHg (e.g., as selected by a user). Note that thesepressures are relative to normal ambient atmospheric pressure thus, −200mmHg would be about 560 mmHg in practical terms. In some embodiments,the pressure range can be between about −40 mmHg and −150 mmHg.Alternatively a pressure range of up to −75 mmHg, up to −80 mmHg or over−80 mmHg can be used. Also in other embodiments a pressure range ofbelow −75 mmHg can be used. Alternatively a pressure range of overapproximately −100 mmHg, or even 150 mmHg, can be supplied by the pumpassembly 150.

In some embodiments, the pump assembly 150 is configured to providecontinuous or intermittent negative pressure therapy. Continuous therapycan be delivered at above −25 mmHg, −25 mmHg, −40 mmHg, −50 mmHg, −60mmHg, −70 mmHg, −80 mmHg, −90 mmHg, −100 mmHg, −120 mmHg, −140 mmHg,−160 mmHg, −180 mmHg, −200 mmHg, or below −200 mmHg. Intermittenttherapy can be delivered between low and high negative pressure setpoints. Low set point can be set at above 0 mmHg, 0 mmHg, −25 mmHg, −40mmHg, −50 mmHg, −60 mmHg, −70 mmHg, −80 mmHg, −90 mmHg, −100 mmHg, −120mmHg, −140 mmHg, −160 mmHg, −180 mmHg, or below −180 mmHg. High setpoint can be set at above −25 mmHg, −40 mmHg, −50 mmHg, −60 mmHg, −70mmHg, −80 mmHg, −90 mmHg, −100 mmHg, −120 mmHg, −140 mmHg, −160 mmHg,−180 mmHg, −200 mmHg, or below −200 mmHg During intermittent therapy,negative pressure at low set point can be delivered for a first timeduration, and upon expiration of the first time duration, negativepressure at high set point can be delivered for a second time duration.Upon expiration of the second time duration, negative pressure at lowset point can be delivered. The first and second time durations can besame or different values. The first and second durations can be selectedfrom the following range: less than 2 minutes, 2 minutes, 3 minutes, 4minutes, 6 minutes, 8 minutes, 10 minutes, or greater than 10 minutes.In some embodiments, switching between low and high set points and viceversa can be performed according to a step waveform, square waveform,sinusoidal waveform, and the like.

In operation, the wound filler 130 is inserted into the wound cavity 110and wound cover 120 is placed so as to seal the wound cavity 110. Thepump assembly 150 provides a source of a negative pressure to the woundcover 120, which is transmitted to the wound cavity 110 via the woundfiller 130. Fluid (e.g., wound exudate) is drawn through the conduit140, and can be stored in a canister. In some embodiments, fluid isabsorbed by the wound filler 130 or one or more absorbent layers (notshown).

Wound dressings that may be utilized with the pump assembly and otherembodiments of the present application include Renasys-F, Renasys-G,Renasys AB, and Pico Dressings available from Smith & Nephew. Furtherdescription of such wound dressings and other components of a negativepressure wound therapy system that may be used with the pump assemblyand other embodiments of the present application are found in U.S.Patent Publication Nos. 2012/0116334, 2011/0213287, 2011/0282309,2012/0136325, 2013/0110058, which are incorporated by reference in theirentireties. In other embodiments, other suitable wound dressings can beutilized.

Pump Assembly and Canister

FIG. 2A illustrates a front view 200A of a pump assembly 230 andcanister 220 according to some embodiments. As is illustrated, the pumpassembly 230 and the canister are connected, thereby forming a device.The pump assembly 230 comprises one or more indicators, such as visualindicator 202 configured to indicate alarms and visual indicator 204configured to indicate status of the TNP system. The indicators 202 and204 can be configured to alert a user to a variety of operating and/orfailure conditions of the system, including alerting the user to normalor proper operating conditions, pump failure, power supplied to the pumpor power failure, detection of a leak within the wound cover or flowpathway, suction blockage, or any other similar or suitable conditionsor combinations thereof. In some embodiments, the pump assembly 230 cancomprise additional indicators. In some embodiments, a single indicatoris used. In other embodiments, multiple indicators are used. Anysuitable indicator can be used such as visual, audio, tactile indicator,and so on. The indicator 202 can be configured to signal alarmconditions, such as canister full (or dressing full in case of acanisterless system), power low, conduit 140 disconnected, seal brokenin the wound seal 120, and so on. The indicator 202 can be configured todisplay red flashing light to draw user's attention. The indicator 204can be configured to signal status of the TNP system, such as therapydelivery is ok, leak detected, and so on. The indicator 204 can beconfigured to display one or more different colors of light, such asgreen, yellow, etc. For example, green light can be emitted when the TNPsystem is operating properly and yellow light can be emitted to indicatea warning.

The pump assembly 230 comprises a display or screen 206 mounted in arecess 208 formed in a case of the pump assembly. In some embodiments,the display 206 can be a touch screen display. In some embodiments, thedisplay 206 can support playback of audiovisual (AV) content, such asinstructional videos. As explained below, the display 206 can beconfigured to render a number of screens or graphical user interfaces(GUIs) for configuring, controlling, and monitoring the operation of theTNP system. The pump assembly 230 comprises a gripping portion 210formed in the case of the pump assembly. The gripping portion 210 can beconfigured to assist the user to hold the pump assembly 230, such asduring removal of the canister 220. In some embodiments, the canister220 can be replaced with another canister, such as when the canister 220has been filled with exudate. The canister 220 can include solidifiermaterial.

The pump assembly 230 comprises one or more keys or buttons 212configured to allow the user to operate and monitor the operation of theTNP system. As is illustrated, in some embodiments, there buttons 212 a,212 b, and 212 c are included. Button 212 a can be configured as a powerbutton to turn on/off the pump assembly 230. Button 212 b can beconfigured as a play/pause button for the delivery of negative pressuretherapy. For example, pressing the button 212 b can cause therapy tostart, and pressing the button 212 b afterward can cause therapy topause or end. Button 212 c can be configured to lock the display 206and/or the buttons 212. For instance, button 212 e can be pressed sothat the user does not unintentionally alter the delivery of thetherapy. Button 212 c can be depressed to unlock the controls. In otherembodiments, additional buttons can be used or one or more of theillustrated buttons 212 a, 212 b, or 212 c can be omitted. In someembodiments, multiple key presses and/or sequences of key presses can beused to operate the pump assembly 230.

The pump assembly 230 includes one or more latch recesses 222 formed inthe cover. In the illustrated embodiment, two latch recesses 222 can beformed on the sides of the pump assembly 230. The latch recesses 222 canbe configured to allow attachment and detachment of the canister 220using one or more canister latches 221. The pump assembly 230 comprisesan air outlet 224 for allowing air removed from the wound cavity 110 toescape. Air entering the pump assembly can be passed through one or moresuitable filters, such as antibacterial filters. This can maintainreusability of the pump assembly. The pump assembly 230 includes one ormore strap mounts 226 for connecting a carry strap to the pump assembly230 or for attaching a cradle. In the illustrated embodiment, two strapmounts 226 can be formed on the sides of the pump assembly 230. In someembodiments, various of these features are omitted and/or variousadditional features are added to the pump assembly 230.

The canister 220 is configured to hold fluid (e.g., exudate) removedfrom the wound cavity 110. The canister 220 includes one or more latches221 for attaching the canister to the pump assembly 230. In theillustrated embodiment, the canister 220 comprises two latches 221 onthe sides of the canister. The exterior of the canister 220 can formedfrom frosted plastic so that the canister is substantially opaque andthe contents of the canister and substantially hidden from plain view.The canister 220 comprises a gripping portion 214 formed in a case ofthe canister. The gripping portion 214 can be configured to allow theuser to hold the pump assembly 220, such as during removal of thecanister from the apparatus 230. The canister 220 includes asubstantially transparent window 216, which can also include graduationsof volume. For example, the illustrated 300 mL canister 220 includesgraduations of 50 mL, 100 mL, 150 mL, 200 mL, 250 mL, and 300 mL. Otherembodiments of the canister can hold different volume of fluid and caninclude different graduation scale. The canister 220 comprises a tubingchannel 218 for connecting to the conduit 140. In some embodiments,various of these features, such as the gripping portion 214, are omittedand/or various additional features are added to the canister 220.

FIG. 2B illustrates a rear view 200B of the pump assembly 230 andcanister 220 according to some embodiments. The pump assembly 230comprises a speaker port 232 for producing and/or radiating sound. Thepump assembly 230 includes a filter access door 234 for accessing andreplacing one or more filters, such as odor filter, antibacterialfilters, etc. In one embodiment, the access door 234 can be used toaccess a chamber (such as a plenum chamber) in which noise suppressingor sound absorbing material is placed. The chamber and sound absorbingmaterial can be part of a silencing system that is used to suppress orabsorb noise generated by the source of negative pressure. Soundabsorbing material can serve to break up sound waves as travel (orreverberate) through the chamber. Sound absorbing material can furtherfunction as an odor suppressant. In one embodiment, for example, soundabsorbing material can be impregnated with activated charcoal for odorsuppression. The access door 234 can further include a seal (such as asealing gasket) for tight closure of the chamber. Additional details ofthe silencing system are described in U.S. Patent Publication No.2010/0185165, which is incorporated by reference in its entirety.

The pump assembly 230 comprises a gripping portion 236 formed in thecase of the pump assembly. As is illustrated, the gripping portion 236is a recess formed in the outer casing of the pump assembly 230. In someembodiments, the gripping portion 236 may include rubber, silicone, etc.coating. The gripping portion 236 can be configured (e.g., positionedand dimensioned) to allow the user to firmly hold the pump assembly 230,such as during removal of the canister 220. The pump assembly 230includes one or more covers 238 configured as screw covers and/or feetor protectors for placing the pump assembly 230 on a surface. The covers230 can be formed out of rubber, silicone, or any other suitablematerial. The pump assembly 230 comprises a power jack 239 for chargingand recharging an internal battery of the pump assembly. In someembodiments, the power jack 239 is a direct current (DC) jack. In someembodiments, the pump assembly can comprise a disposable power source,such as batteries, so that no power jack is needed.

The canister 220 includes one or more feet 244 for placing the canisteron a surface. The feet 244 can be formed out of rubber, silicone, or anyother suitable material and can be angled at a suitable angle so thatthe canister 220 remains stable when placed on the surface. The canister220 comprises a tube mount relief 246 configured to allow one or moretubes to exit to the front of the device. The canister 220 includes astand or kickstand 248 for supporting the canister when it is placed ona surface. As explained below, the kickstand 248 can pivot between anopened and closed position. In closed position, the kickstand 248 can belatched to the canister 220. In some embodiments, the kickstand 248 canbe made out of opaque material, such as plastic. In other embodiments,the kickstand 248 can be made out of transparent material. The kickstand248 includes a gripping portion 242 formed in the kickstand. Thegripping portion 242 can be configured to allow the user to place thekickstand 248 in the closed position. The kickstand 248 comprises a hole249 to allow the user to place the kickstand in the open position. Thehole 249 can be sized to allow the user to extend the kickstand using afinger.

FIG. 2C illustrates a view 200C of the pump assembly 230 separated fromthe canister 220 according to some embodiments. The pump assembly 230includes a vacuum attachment or connector 252 through which a vacuumpump communicates negative pressure to the canister 220. The connector252 can correspond to the inlet of the pump assembly. The pump assembly230 comprises a USB access door 256 configured to allow access to one ormore USB ports. In some embodiments, the USB access door is omitted andUSB ports are accessed through the door 234. The pump assembly 230 caninclude additional access doors configured to allow access to additionalserial, parallel, and/or hybrid data transfer interfaces, such as SD,Compact Disc (CD), DVD, FireWire, Thunderbolt, PC1 Express, and thelike. In other embodiments, one or more of these additional ports areaccessed through the door 234.

FIG. 2D illustrates a view 200D of the interior components of the pumpassembly 230 according to some embodiments. The pump assembly 230 caninclude various components, such as a canister connector 252 whichincludes a sealing ring 253, control printed circuit board (PCB) 260,peripherals PCB 262 (e.g., for USB connectivity), power supply PCB 264,vacuum pump 266, power supply 268 (e.g., rechargeable battery), speaker270, and light guide or pipe 272 (e.g., for status indication usingguided light emitted by one or more LEDs). Further details of statusindication are provided in U.S. Pat. No. 8,294,586, which isincorporated by reference in its entirety. Other components can beincluded, such as electrical cables, connectors, tubing, valves,filters, fasteners, screws, holders, and so on. In some embodiments, thepump assembly 230 can comprise alternative or additional components.

FIG. 2E illustrates another view 200E of the interior components of thepump assembly 230 according to some embodiments. As is explained below,the pump assembly 230 includes an antenna 276. The connector 252 betweenthe vacuum pump 266 and the canister 220 includes a flow restrictor 278.As is explained below, the flow restrictor 278 can be a calibrated flowrestrictor used for measuring flow in the fluid flow path and fordetermining various operating conditions, such as leaks, blockages, highpressure (over-vacuum), and the like. In some embodiments, flow acrossthe restrictor 278 can be determined by measuring a pressuredifferential (or pressure drop) across the flow restrictor. In variousembodiments, flow across the restrictor 278 can be characterized as highflow (e.g., due to a leak), low flow (e.g., due to a blockage orcanister being full), normal flow, etc. As is illustrated, pressuresensor 284 measures pressure upstream (or on the canister side) of theflow restrictor 278. Pressure sensor 284 can be an electronic pressuresensor mounted on the control PCB 264. Conduit or lumen 286 can connectthe upstream side of the flow restrictor 278 with the pressure sensor284. Pressure sensors 280 and 282 measure pressure downstream (or on thevacuum pump side) of the flow restrictor 278. Pressure sensors 280 and282 can be electronic pressure sensors mounted on the control PCB 264.Conduit or lumen 288 can connect the downstream side of the flowrestrictor 278 with the pressure sensors 280 and 284 via a Y-connector289.

In some embodiments, one of pressure sensors 280 and 282 can bedesignated as a primary pressure sensor and the other as a backuppressure sensor in case the primary pressure sensor becomes defective orinoperative. For example, pressure sensor 280 can be the primarypressure sensor and pressure sensor 282 can be the backup pressuresensor. Pressure drop across the flow restrictor 278 can be determinedby subtracting pressure measured by sensor 280 and sensor 284. Ifpressure sensor 280 fails, pressure drop across the flow restrictor canbe determined by subtracting pressure measured by sensor 282 and sensor284. In certain embodiments, the backup pressure sensor can be used formonitoring and indicating high pressure conditions, that is when thepressure in the flow path exceeds a maximum pressure threshold. In someembodiments, one or more differential pressure sensors can be used. Forexample, a differential pressure sensor connected to the upstream anddownstream sides of the flow restrictor 278 can measure the pressuredrop across the flow restrictor. In some embodiments, one or more ofthese components, such as the flow restrictor 278, are omitted and/oradditional components, such as one or more flow meters, are used.

Flow Rate Monitoring

FIG. 3 illustrates a fluid flow path 300A according to some embodiments.The flow path 300A includes a wound cavity 310, canister 320, pressuresensor 330, and source of negative pressure 340. The flow of fluid isfrom left to right (e.g., from the wound 310 to the negative pressuresource 340). FIG. 3 illustrates a fluid flow path 300B according to someembodiments. The flow path 300B includes the wound 310 cavity, pressuresensor 330, canister 320, and source of negative pressure 340. The flowof fluid is from left to right (e.g., from the wound cavity 310 to thenegative pressure source 340). As is illustrated, the difference betweenflow paths 300A and 300B is the positioning of the pressure sensor 330.In fluid flow path 300A the pressure sensor 330 is located downstream ofthe canister 320 (e.g., at the inlet of the negative pressure source340), while in the fluid flow path 300B the pressure sensor 330 islocated upstream of the canister 320.

Some embodiments of the system monitor and/or determine a rate of flowof fluid in the system. In certain embodiments, flow rate monitoring canbe performed by a controller or processor. Monitoring the flow rate canbe used, among other things, to ensure that therapy is properlydelivered to the wound, to detect blockages, canister full (or dressingfull in case of a canisterless system) conditions, and/or leaks in thefluid flow path, high pressure, ensure that the flow rate is not unsafe(e.g., dangerously high), etc.

In some embodiments, the system performs flow rate monitoring indirectlyby measuring and/or monitoring activity of the negative pressure source.For example, speed of vacuum pump motor can be measured, such as, byusing a tachometer. A pump control processor can continuously monitorthe pump speed using the tachometer feedback from the pump. If pumpspeed falls below a threshold value over a particular period of time,such as 2 minutes, it can be determined that a blockage is present inthe flow path, particularly in systems in which an minimum pump speed isexpected (e.g., due to a presence of a controlled leak). The blockagecan be due to a blockage in a tube or lumen, canister (or dressing)being full, etc. An alarm can be triggered and the system can wait forthe user to take one or more actions to resolve the blockage. In someembodiments, activity of the negative pressure source can be measured byone or more other suitable techniques, such as by using a pump speedsensor (e.g., Hall sensor), measuring back EMF generated by the pumpmotor, and the like. A pump control processor can continuously monitorvoltage and/or current at which the pump is being driven, and determinethe activity of the negative pressure source based on the monitoredvoltage and/or current and load on the pump. In some embodiments, pulsefrequency (e.g., pressure signal frequency) can be monitored (e.g.,using one or more pressure sensors) to determine the activity of thenegative pressure source. For example, a count of pressure pulses can beused as an indicator of the activity of the negative pressure source.

In various embodiments, tachometer can be read periodically, such asevery 100 msec, and periodic readings made over a time duration, such as2.5 seconds, 32 second, or any other suitable duration can be combined(e.g., averaged). Combined tachometer readings can be used for leakdetection, blockage detection, limiting the maximum flow rate, etc.Combined tachometer readings (e.g., in counts) can be converted to aflow rate (e.g., in mL/min) using one or more conversion equationsand/or tables so that a current flow rate is determined. In someembodiments, the flow rate is determined according to the followingequation:FR=C ₁ *F*P+C ₂

where FR is the flow rate, F is the frequency of the pump tachometersignal, P is pressure produced by the pump (or pressure setpoint), andC₁ and C₂ are suitable constants. The determined flow rate can becompared to various flow rate thresholds, such as blockage threshold,leakage threshold, and maximum flow rate threshold, to determine apresence of a particular condition, such as a blockage, leakage, andover-vacuum.

Other suitable ways for determining flow rate can be used. For example,the flow rate can be periodically computed, such as every 250milliseconds or any other suitable time value, according to thefollowing formula:FR=Slope*Tachometer+Intercept

where Tachometer is an average of tachometer readings (e.g., in Hz),such as over last 2.5 second or any other suitable period of time, andSlope and Intercept are constants that are based on the pressuresetpoint. The values for Slope and Intercept can be determined forpossible pressure setpoints (e.g., −25 mmHg, −40 mmHg, −50 mmHg, 60mmHg, −70 mmHg, −80 mmHg, −90 mmHg, −100 mmHg, −120 mmHg, −140 mmHg, 160mmHg, −180 mmHg, −200 mmHg) for a given vacuum pump type. The flow as afunction of the pump speed may not be a best fit as a single linebecause the vacuum pump can be designed to be more efficient at lowerflow rates. Because of this, slope and intercept values can bepre-computed for various setpoints and various pumps. Flow rate can bemeasured in standard liters per minute (SLPM) or any other suitablemeasurement unit.

In some embodiments, a blockage condition is detected when thedetermined flow rate falls below a blockage threshold. A blockage alarmcan be enabled if the blockage condition is present over a period oftime, such as 30 seconds. The blockage alarm can be disabled when thedetermined flow rate exceeds the blockage threshold. In someembodiments, the system can differentiate between a blockage in a tubeor lumen and canister (or dressing) full conditions. In someembodiments, a leakage condition is detected when the determined flowrate exceeds a leakage threshold. A leakage alarm can be enabled if theleakage condition is present over a period of time, such as 30 seconds.The leakage alarm can be disabled when the detected flow rate fallsbelow the leakage threshold. In some embodiments, in order to prevent anover-vacuum condition, a maximum flow rate is imposed, such as 1.6liters/min. Pump drive signal, such as voltage or current signal, can belimited not exceed the flow rate threshold.

In certain embodiments, one or more pressure sensors can be placed insuitable locations in the fluid flow path. Pressure measured by the oneor more sensors is provided to the system (e.g., pump control processor)so that it can determine and adjust the pump drive signal to achieve adesired negative pressure level. The pump drive signal can be generatedusing PWM. Additional details of flow rate detection and pump controlare provided in U.S. Patent Application No. 2013/0150813, which isincorporated by reference in its entirety.

In some embodiments, flow rate monitoring is performed by measuring flowthrough a flow restrictor placed in a portion of the fluid flow path. Incertain embodiments, flow restrictor 278 illustrated in FIG. 2E can beused. The flow restrictor can be calibrated such that it can be used toreliably monitor flow rate for different types of wounds, dressings, andoperating conditions. For example, a high precision silicon flowrestrictor can be used. As another example, the flow restrictor can bebuilt using other suitable materials. The flow restrictor can be locatedat any suitable location in the flow path, such as between the source ofthe negative pressure and the canister, such as upstream of the sourceof the negative pressure and downstream of the canister. A differentialpressure sensor or two pressure sensors can be used to measure apressure drop across the flow restrictor. For example, as explainedabove in connection with FIG. 2E, the pressure drop across the flowrestrictor 278 can be measured using sensors 282 and 284. In certainembodiments, if the pressure drop falls below a pressure differentialthreshold, which indicates low flow, the measured flow rate is comparedto a flow rate threshold. If the measured flow rate falls below the flowrate threshold, blockage condition is detected. Additional details ofblockage detection are provided in U.S. Patent Publication No.2011/0071483, which is incorporated by reference in its entirety. Insome embodiments, the measured flow rate is compared to a leakagethreshold. If the measured flow rate exceeds the leakage threshold, aleak is detected. Additional details of leakage detection are providedin U.S. Pat. No. 8,308,714, which is incorporated by reference in itsentirety.

Blockage Detection

In some embodiments, blockages and presence of exudate in one or moretubes or lumens are detected by processing data from one or morepressure sensors, such as sensors 280, 282, and 284. This detection canbe enhanced by changing one or more settings of the vacuum pump, such asincreasing vacuum level delivered by the pump, decreasing the vacuumlevel, stopping the pump, changing the pump speed, changing a cadence ofthe pump, and the like. In some embodiments, as the pump operates, itgenerates pressure pulses or signals that are propagated through thefluid flow path. The pressure signals are illustrated in the pressurecurve 402 of FIG. 4 according to some embodiments. As is illustrated inregion 404, pressure in the fluid flow path varies or oscillates arounda particular pressure setting or set point 408 (e.g., as selected by theuser) during normal operation of the system. Region 406 illustratespressure pulses in the flow path when there is a blockage distal to thenegative pressure source, such as the canister (or dressing) becomesfull and/or a canister filter is occluded or blocked. As is illustrated,a distal blockage causes a reduced volume to be seen upstream of thecanister (or dressing), and the amplitude of the pressure pulsesincreases. The frequency of a pressure signal is slowed or decreased insome embodiments. In certain embodiments, this change or “bounce” in themagnitude (or frequency) of the pressure pulse signal can be magnifiedor enhanced by varying the pump speed, varying the cadence of the pump,such as by adjusting PWM parameters, and the like. Such adjustments ofpump operation are not required but can be performed over short timeduration and the changes can be small such that the operation of thesystem remains relatively unaffected. In some embodiments, the canisterfilter can be hydrophobic so that the flow of liquid is substantiallyblocked while the flow of air is allowed. Additional details of flowrate detection are described in U.S. Patent Publication No.2012/0078539, which is incorporated by reference in its entirety.

In some embodiments, canisterless systems use absorbent dressing forexudate removed from the wound. Such dressing may include absorbing orsuperabsorbing material to collect and/or retain exudate so that it isnot aspirated into the negative pressure source. Similar to a canisterfilter, a dressing filter (which may be hydrophobic) may be used toprevent the exudate from reaching the negative pressure source. In suchsystems, detection of a dressing full condition or dressing filter(which may be) occluded condition can be an equivalent to detection of acanister full condition.

In some embodiments, changes in characteristics of pressure signals canbe used to determine distal blockages, level of exudate in the canister(or dressing), canister (or dressing) full conditions, and the like. Thecharacteristics can include signal magnitude, frequency, shape (e.g.,envelope), etc. In some embodiments, the system can detect canister (ordressing) pre-full condition or the level of exudate in the canister (ordressing) reaching a certain threshold, which may be less than beingapproximately 100% full. For example, the system can detect the canister(or dressing) being 75% full, 80% full, 95%, and so on. Advantageously,such detection mechanisms can provide earlier indication of the need tochange the canister (or dressing) and avoid prolonged interruption ofthe delivery of therapy. Sensitivity of alarms can be increased. Invarious embodiments, the level of a leak in present in the fluid flowpath does not affect accurate determination of the level of exudate inthe canister and/or detection of the canister (or dressing) pre-full orfull conditions.

FIGS. 5A-5D illustrates graphs of pressure signals according to someembodiments. The illustrated graphs can correspond to a particularpressure setting, such as 40 mmHg. The illustrated graphs can alsocorrespond to various leak levels of leak rates in the system. Forexample, FIG. 5A may correspond to 60 mL/min leak (e.g., low leak), FIG.5B may correspond to a 150 mL/min leak, FIG. 5C may correspond to a 450mL/min leak, and FIG. 5D may correspond to a 1000 mL/min leak (e.g.,very high leak). FIG. 5A illustrates a magnitude curve 502A of thepressure signal in the flow path as sensed by one or more pressuresensors over a period of time. Curve 502A can correspond to a signalobserved when the canister is relatively empty. For example, thecanister may be configured to hold up to 750 mL fluid volume, and curve502A can correspond to the empty volume of 515 mL. As is illustrated,the bounce in the pressure signal magnitude curve 502A is relativelysmall as the curve is substantially flat. The bounce of the pressuresignal can be measured using a variety of techniques, such as bymeasuring peak-to-trough change and selecting the largest such change asbeing indicative of the largest bounce. Curve 502A can correspond to thevoltage reading, current reading, etc. Curve 504A corresponds to a pumpspeed signal (e.g., as measured by a tachometer, PWM signal, etc.).

FIG. 5B illustrates a magnitude curve 502B of the pressure signal in theflow path as sensed by one or more pressure sensors over a period oftime. Curve 502B can correspond to a signal observed when the canisteris relatively full. For example, the canister may be configured to holdup to 750 mL volume, and curve 502B can correspond to the empty volumeof 60 mL. As is illustrated, the bounce in the pressure signal magnitudecurve 502B is larger than that in curve 502A. Curve 504B corresponds tothe pump speed signal. FIG. 5C illustrates a magnitude curve 502C of thepressure signal in the flow path as sensed by one or more pressuresensors over a period of time. Curve 502C can correspond to a signalobserved when the canister is almost full. For example, the canister maybe configured to hold up to 750 mL volume, and curve 502C can correspondto the empty volume of 30 mL. As is illustrated, the bounce in thepressure signal magnitude curve 502B is larger than that in curves 502Aand 502B. Curve 504C corresponds to the pump speed signal.

FIG. 5D illustrates a magnitude curve 502D of the pressure signal in theflow path as sensed by one or more pressure sensors over a period oftime. Curve 502D can correspond to a signal observed when the canisteris nearly full. For example, the canister may be configured to hold upto 750 mL volume, and curve 502D can correspond to the empty volume of15 mL. As is illustrated, the bounce in the pressure signal magnitudecurve 502D is larger than that in curves 502A, 502B, and 502C. Curve504D corresponds to the pump speed signal.

Table 1 illustrates the largest magnitude bounces or peak-to-troughchanges (e.g., in voltage as indicated by V_(p-p)) measured for thecurves 502A, 502B, 502C, and 502D according to some embodiments. Withreference to the first row (row 1), column A corresponds to curve 502Aand indicates the largest change of 0.010 V, column B corresponds tocurve 502D and indicates the largest change of 0.078 V, column Ccorresponds to curve 502C and indicates the largest change of 0.122 V,and column D corresponds to curve 502D and indicates the largest changeof 0.170 V. These increasing bounce values confirm that the bounce inthe pressure signal magnitude increases as the canister fills up. Levelof exudate in the canister (or the dressing) can be detected bycomparing the determined pressure magnitude bounce to one or moremagnitude thresholds, which can be determined experimentally forcanisters (or dressing) of various sizes. For example, canister (ordressing) pre-full condition may be set to the canister having 30 mL orless empty volume. Using Table 1, a pre-full threshold can be set toapproximately 0.12 V peak-to-trough bounce. In some embodiments,measures other than or in addition to peak-to-trough can be used, suchas average bounce, etc.

TABLE 1 Pressure Magnitude Bounce at 40 mmHg D C B A Pressure Magnitude15 mL 30 mL 60 mL 515 mL (V_(p-p)) at 40 mmHg volume volume volumevolume 1 60 mL/min 0.170 0.122 0.078 0.010 2 150 mL/min 0.174 0.1200.074 0.012 3 450 mL/min 0.178 0.118 0.068 0.008 4 1000 mL/min 0.1240.082 0.050 0.012

In some embodiments, signal processing techniques can be utilized on thedetected pressure signal. For example, sensed pressure values can beprocessed, such as low-pass filtered (e.g., via averaging), to removenoise. As another example, detected pressure signal can be convertedinto frequency domain, for example by using the Fast Fourier Transform(FFT). The signal can be processed and analyzed in frequency domain.

FIGS. 6A-6D illustrates graphs of pressure signals according to someembodiments. Similar to FIGS. 5A-5D, these graphs illustrate pressuremagnitude curves and pump speed curves at 150 mL/min leak for unfilledcanister volumes of 515 mL, 60 mL, 30 mL, and 15 mL. As is illustratedin FIGS. 6A-6D and confirmed by the values in the second row (row 2) ofTable 1, the bounce in the pressure signal increases as the canisterfills up. FIGS. 7A-7D illustrates graphs of pressure signals accordingto some embodiments. Similar to FIGS. 5A-5D, these graphs illustratepressure magnitude curves and pump speed curves at 450 mL/min leak forunfilled canister volumes of 515 mL, 60 mL, 30 mL, and 15 mL. As isillustrated in FIGS. 7A-7D and confirmed by the values in the third row(row 3) of Table 1, the bounce in the pressure signal increases as thecanister fills up. FIGS. 8A-8D illustrates graphs of pressure signalsaccording to some embodiments. Similar to FIGS. 5A-5D, these graphsillustrate pressure magnitude curves and pump speed curves at 1000mL/min leak (which is a very high leak) for unfilled canister volumes of515 mL, 60 mL, 30 mL, and 15 mL. As is illustrated in FIGS. 8A-8D andconfirmed by the values in the fourth row (row 4) of Table 1, the bouncein the pressure signal increases as the canister fills up. From theillustrations in FIGS. 5-8 and the values in Table 1, it can be seenthat detection of the level of exudate in the canister (or in thedressing) and/or canister (or dressing) pre-full condition can beperformed irrespective of the leak rate in the fluid flow path.

As is illustrated in FIGS. 5-8 and Table 1, the bounce or ripple in theobserved pressure magnitude increases as the canister fills up and thevolume “seen” by the pump decreases. FIG. 9 illustrates sensed pressuremagnitude ripple according to some embodiments. The y-axis representslargest peak-to-trough voltage changes. The x-axis corresponds tocanister unfilled volumes (e.g., volume ahead or upstream of the pump).A 750 mL, canister is used according to some embodiments. There are fourcurves illustrated corresponding to target pressure settings of 40 mmHg,80 mmHg, 120 mmHg, and 200 mmHg. Vertical bars on the curves representvariation resulting from the changes to the leak rate. Table 2illustrates the plotted values according to some embodiments. As isillustrated in FIG. 9 and Table 2, magnitude of the pressure bounceincreases as the canister becomes full irrespective of the leak rate forvarious pressure settings.

TABLE 2 15 mL 30 mL 60 mL 515 mL V_(p-p) * volume volume volume volume40 mmHg 0.174 ± 0.120 ± 0.073 ± 0.010 ± 0.008 0.004 0.010 0.004 80 mmHg0.119 ± 0.081 ± 0.049 ± 0.008 ± 0.015 0.006 0.002 0.000 120 mmHg 0.095 ±0.061 ± 0.037 ± 0.006 ± 0.005 0.005 0.002 0.000 200 mmHg 0.056 ± 0.037 ±0.027 ± 0.008 ± 0.000 0.009 0.009 0.000 (* 1000 mL/min data wasexcluded)

In some embodiments, thresholds for determining the level of exudate inthe canister (or the dressing) and/or canister (or dressing) pre-fullcondition can be determined for various pressure settings and variouscanister volumes. For example, Table 3 illustrates the largest magnitudebounces or peak-to-trough changes for 80 mmHg pressure setting accordingto some embodiments. Similar tables can be constructed for otherpossible pressure settings. Level of exudate in the canister/dressing(and, accordingly, a measure of how empty the canister/dressing is),canister/dressing pre-full condition, and/or canister/dressing fullcondition can be determined at run time by loading a table correspondingto a particular selected pressure setting and comparing the monitoredpressure signal magnitude bounce to one or more thresholds. Othersuitable data structures can be used in place of a table, such as array,list, index, graph, etc.

TABLE 3 Pressure Magnitude Bounce at 80 mmHg D C B A Pressure Magnitude15 mL 30 mL 60 mL 515 mL (V_(p-p)) at 80 mmHg volume volume volumevolume 1 60 mL/min 0.114 0.078 0.048 0.008 2 150 mL/min 0.116 0.0840.050 0.008 3 450 mL/min 0.128 0.080 0.050 0.008 4 1000 mL/min 0.0920.058 0.034 0.010

In some embodiments, frequency of the detected pressure signal can beused in addition to or instead of changes in amplitude for detection ofcanister (or dressing) pre-full conditions and/or for determining thelevel of exudate in the canister (or dressing). For example, Table 4illustrates pressure signal frequencies at 40 mmHg pressure setting forvarious unfilled canister volumes at various leak rates according tosome embodiments. As is shown in Table 4, the frequency of the detectedpressure signal decreases or drops as the canister becomes full (e.g.,compare column A corresponding to 515 mL unfilled canister volume tocolumn D corresponding to 15 mL unfilled canister volume). This changein the frequency is observed irrespective of the leak rate. Thefrequency of the detected pressure signal can be compared to one or morefrequency thresholds, which may be determined experimentally, to detectcanister (or dressing) pre-full condition and/or detect the level ofexudate in the canister (or dressing).

TABLE 4 Pressure Signal Frequency at 40 mmHg D C B A Pressure Frequencyat 15 mL 30 mL 60 mL 515 mL 40 mmHg (Hz) volume volume volume volume 160 mL/min 2.59 2.67 2.67 2.62 2 150 mL/min 3.51 3.76 3.75 3.53 3 450mL/min 6.62 6.94 6.99 6.94 4 1000 mL/min 13.16 12.99 12.66 13.89

In some embodiments, similar tables can be constructed for otherpossible pressure settings. For example, Table 5 illustrates pressuresignal frequencies at 80 mmHg pressure setting for various unfilledcanister volumes at various leak rates according to some embodiments.Level of exudate in the canister (or dressing), canister (or dressing)pre-full condition, and/or canister (or dressing) full condition can bedetermined at run time by loading a table (or another suitable datastructure) corresponding to a particular selected pressure setting andcomparing the monitored pressure signal frequency to one or morethresholds. The thresholds can be determined experimentally for variouscanister (or dressing) volumes.

TABLE 5 Pressure Signal Frequency at 80 mmHg D C B A Pressure Frequencyat 15 mL 30 mL 60 mL 515 mL 80 mmHg (Hz) volume volume volume volume 160 mL/min 3.76 3.83 3.82 3.82 2 150 mL/min 4.98 4.67 4.81 4.88 3 450mL/min 8.26 8.47 8.26 8.20 4 1000 mL/min 15.38 15.63 15.15 15.87

In some embodiments, additional attributes can be used for canister (ordressing) pre-full detection and/or determination of the level ofexudate in the canister (or dressing). For example, flow rate throughthe flow path can be used in addition to analyzing the pressuremagnitude. In some embodiments, flow rate can be measured indirectly bymeasuring and analyzing the pump speed as is disclosed in U.S. PatentPublication No. 2012/0001762, which is incorporated by reference in itsentirety. In some embodiments, flow rate can be measured directly byusing a flow meter. In some embodiments, increase in the pressuremagnitude bounce and decrease in the flow rate (e.g., pump speed, suchas reflected by a slowing tachometer) indicates a canister (or dressing)full condition. Decrease in the pump speed alone may not be a reliableindicator of the canister full condition as such decrease can be causedby an improved seal and resulting lowering of the leak rate. Inaddition, presence of a small leak in the flow path may cause the pumpto continue working even though the canister may be nearly full orfrill, which can cause inaccurate detection of the canister fullcondition.

In some embodiments, detection of canister (or dressing) pre-full and/orfull conditions using the characteristics of the pressure signals canallow the system to differentiate between blockage conditions in thefluid flow path and blockages in the canister (or in the dressing). Insome embodiments, alarm sensitivity is improved. For example, canisterfull detection mechanisms in systems that do not use characteristics ofthe pressure signal may rely solely on the flow rate measurements (e.g.,as indicated by pump speed measurements) for determining whether thecanister is full. Using characteristics of the pressure signal asdisclosed herein can trigger the canister frill alarm much earlier, suchas for example 20 or more minutes earlier. Advantageously, improvingalarm sensitivity can result in increasing safety and patient comfort asthe canister can be changed timely before it becomes full and therapy isinterrupted.

FIG. 10 illustrates a process 1000 of detecting proximal blockagesaccording to some embodiments. The process 1000 can be implemented by acontroller of processor. The process 1000 measures one or more pressuresignal characteristics in block 1002. For example, pressure signalmagnitude, frequency, etc. can be measured. In block 1004, the process1000 removes noise from the one or more measured pressure signalcharacteristics. For example, the pressure signal can be low passfiltered. In block 1006, the process 1000 compares the one or morepressure signal characteristics to one or more thresholds. If in block1008 the process 1000 determines that the one or more thresholds havebeen satisfied (e.g., exceeded), the process transitions to block 1012where it determines that there is a proximal blockage (e.g., due to thecanister being full). The process 1000 can activate one or more alarmsor indicators. If in block 1008 the process 1000 determines that the oneor more thresholds have not been satisfied (e.g., not exceeded), theprocess transitions to block 1010 where it determines that there is noproximal blockage. In some embodiments, the process 1000 can usehysteresis in block 1008. For example, the process 1000 can transitionto block 1012 provided that a threshold has been met (e.g., exceeded)for a duration or period of time. In some embodiments, the one or morethresholds utilized by the process 1000 can be selected to determinecanister (or dressing) pre-full condition and/or a particular level ofexudate in the canister (or dressing). Process 1000 can be implementedby systems with canisters or by canisterless systems.

In some embodiments, canister (or dressing) full condition can bedetected as follows. A plurality of pressure sensor readings, eachperformed over a time duration (e.g., 2 seconds or any other suitableduration which may be vary between sample periods), are collected. Anumber of readings of the plurality of readings, such as 25 sampleperiods out of 30 or any other suitable number, are checked to determineif each indicates that the canister is full. This can performed bydetermining maximum and minimum pressure values captured over the timeduration of a particular sample period. The values can be voltagevalues, current values, or any other suitable values that correspond topressure. A difference between maximum and minimum values for aparticular sample period corresponds to peak-to-through pressure (whichis indicative of change in pressure pulse amplitude). If it isdetermined that the peak-to-through pressure for a particular sampleperiod exceeds a threshold pressure value, then the particular sampleperiod indicates that the canister is full.

The threshold value can be any suitable pressure threshold, such as avalue selected or determined based on the negative pressure setpoint andthe current level of activity of the pump, which as explained above canbe determined using a tachometer average (such as averaged tachometerreadings or any other suitable measure of the flow rate). For example,threshold values listed in Table 1 can be used for comparing topeak-to-through pressure. These values correspond to a particular pumpmotor and particular pressure sensor.

TABLE 6 Threshold values for detecting canister full conditionTachometer Frequency Peak-to-Through Pressure Setpoint (in Hz) (in mV)(in mmHg) Low Med High Low Med High 25 17 25 <25 50 110 215 40 23 35 <3575 135 220 50 30 50 <50 90 175 225 60 30 55 <55 80 185 225 70 40 60 <60115 185 235 80 40 60 <60 100 165 235 90 45 65 <65 110 170 235 100 45 65<65 105 165 235 120 45 75 <75 105 175 235 140 50 85 <85 110 190 235 16060 90 <90 110 165 220 180 75 100 <100 130 165 220 200 75 100 <100 125155 210

Canister full determination can be performed on a sliding window basis.For example, a sliding window of 25 out of 30 sample periods can beanalyzed and if 25 sample periods are determined to indicate that thecanister is full, the pump concludes that the canister (or dressing) isfull. Assuming that the sample period is 2 seconds, using a slidingwindow of 25 out of 30 sample periods effectively results in determiningwhether change in pressure pulse amplitude exceeds the threshold for 60seconds. If the tachometer average becomes greater than a leak threshold(e.g., flow rate associated with presence of a leak in the flow path) orcanister pressure (as measured by a pressure sensor) becomes less than alow vacuum pressure threshold (e.g., flow rate associated with a lowvacuum condition in the flow path), canister full detection can besuspended or terminated. For example, if a sliding window of 25 out of30 sample periods with each sample period having duration of 2 secondsin used, 60 second timer for canister full detection can be reset whenit has been determined that the tachometer average becomes greater thanthe leak threshold or canister pressure becomes less than the low vacuumpressure threshold. This can prevent generation of unnecessary andundesirable alarms.

Alternatively or additionally, canister full condition can be detectedif a single sample period indicates that the canister is full. However,performing canister full detection using a plurality of sample periodscan mitigate the effects of one or more transient conditions in thefluid flow path or one or more errant pressure readings. Alternativelyor additionally, canister full detection can be performed by measuringthe frequency of detected pressure signal and comparing the measuredfrequency to one or more suitable thresholds.

In some embodiments, additional or alternative mechanisms can be usedfor detecting proximal blockages. One or more additional pressuresensors can be used to measure differential pressure across the canister(e.g., at the canister inlet and outlet). One or more additionalconduits (e.g., dual lumens) can be used to inject a signal through onelumen for detection by another lumen. Flow rate can be measured directlyor indirectly and used for canister blockage detection. A bias leak canbe introduced into the flow path and maintained such that flow ratedropping below the bias leak rate indicates a presence of a blockage inthe flow path. Optical sensors, ultrasonic sensors, and/or weightsensors can be used to determine the level of exudate in the canister(or dressing). Lasers can also be used. One or more sensors that are notrelated to measuring pressure and/or flow, such as a capacitive sensoror a strain gauge, can be used.

In some embodiments, temporary blockages caused by slugs or boluses offluid in tubes and/or lumens are detected by turning off the pump andmonitoring the pressure change in the fluid flow path. The pump can beturned off for a short duration of time as to not affect the operationof the system. Presence of temporary blockages in the system due toboluses of fluid can cause a detectable difference in pressure decay inthe device including a discontinuous “stair and risers” pattern in asystem with a distal leak. Such discontinuous decaying pattern may bedue to boluses of fluid moving through the fluid flow path and arrivingat the canister inlet, which can suddenly change the volume seen by thepressure sensor (and the canister or the dressing). When boluses offluid are not present, a more continuous decaying pattern may be isobserved. In certain embodiments, when the discontinuous “stairs andrisers” pattern is detected, the system can increase the level of vacuumproduced by the pump to clear the boluses. An alarm can be asserted ifthe tubes and/or lumens cannot be cleared.

In some embodiments, one or more flow sensors and/or flow meters can beused to directly measure the fluid flow. In some embodiments, the systemcan utilize one or more of the foregoing flow rate monitoringtechniques. The system can be configured to suitably arbitrate betweenflow rates determined using multiple flow rate monitoring techniques ifone or more such techniques are executed in parallel. In certainembodiments, the system execute one of the techniques, such as the flowrate determination based on the pump speed, and utilize one or moreother techniques as needed. In various embodiments, the system canutilize one or more other techniques in cases the determined flow rateor flow path condition is perceived to be inaccurate or unreliable. Insome embodiments, the system can utilize one or more of the techniquesto detect a sudden change in a flow rate suggesting change to thedressing leak characteristics (e.g., a greater flow indicates thedevelopment of a leak and a lesser flow indicating a sudden restrictionor blockage).

Other Variations

Any value of a magnitude, frequency, threshold, limit, duration, etc.provided herein and/or illustrated in the figures is not intended to beabsolute and, thereby, can be approximate. In addition, any magnitude,frequency, threshold, limit, duration, etc. provided herein and/orillustrated in the figures can be fixed or varied either automaticallyor by a user. Moreover, any value of a magnitude, frequency, threshold,limit, duration, etc. provided herein and/or illustrated in the figuresis illustrative and can change depending on an embodiment. For example,the values provided in the tables (Tables 1-5) can vary depending oncanister (or dressing) volume, sensor range, etc. Furthermore, as isused herein relative terminology such as exceeds, greater than, lessthan, etc. in relation to a reference value is intended to alsoencompass being equal to the reference value. For example, exceeding areference value that is positive can encompass being equal to or greaterthan the reference value. In addition, as is used herein relativeterminology such as exceeds, greater than, less than, etc. in relationto a reference value is intended to also encompass an inverse of thedisclosed relationship, such as below, less than, greater than, etc. inrelations to the reference value.

Features, materials, characteristics, or groups described in conjunctionwith a particular aspect, embodiment, or example are to be understood tobe applicable to any other aspect, embodiment or example describedherein unless incompatible therewith. All of the features disclosed inthis specification (including any accompanying claims, abstract anddrawings), and/or all of the steps of any method or process so disclosed(such as the process illustrated in FIG. 10), may be combined in anycombination, except combinations where at least some of such featuresand/or steps are mutually exclusive. The protection is not restricted tothe details of any foregoing embodiments. The protection extends to anynovel one, or any novel combination, of the features disclosed in thisspecification (including any accompanying claims, abstract anddrawings), or to any novel one, or any novel combination, of the stepsof any method or process so disclosed.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of protection. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms. Furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made. Those skilled in the art willappreciate that in some embodiments, the actual steps taken in theprocesses illustrated and/or disclosed may differ from those shown inthe figures. Depending on the embodiment, certain of the steps describedabove may be removed, others may be added. For example, the actual stepsand/or order of steps taken in the disclosed processes may differ fromthose shown in the figure. Depending on the embodiment, certain of thesteps described above may be removed, others may be added. For instance,the various components illustrated in the figures may be implemented assoftware and/or firmware on a processor, controller, ASIC, FPGA, and/ordedicated hardware. Furthermore, the features and attributes of thespecific embodiments disclosed above may be combined in different waysto form additional embodiments, all of which fall within the scope ofthe present disclosure.

User interface screens illustrated and described herein can includeadditional and/or alternative components. These components can includemenus, lists, buttons, text boxes, labels, radio buttons, scroll bars,sliders, checkboxes, combo boxes, status bars, dialog boxes, windows,and the like. User interface screens can include additional and/oralternative information. Components can be arranged, grouped, displayedin any suitable order.

Although the present disclosure includes certain embodiments, examplesand applications, it will be understood by those skilled in the art thatthe present disclosure extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses and obviousmodifications and equivalents thereof, including embodiments which donot provide all of the features and advantages set forth herein.Accordingly, the scope of the present disclosure is not intended to belimited by the specific disclosures of preferred embodiments herein, andmay be defined by claims as presented herein or as presented in thefuture.

What is claimed is:
 1. A wound therapy apparatus comprising: a pressure source configured to be in fluid communication with a wound dressing that is positioned over a wound; a canister configured to be in fluid communication with the wound dressing and the pressure source via a fluid flow path, the canister being configured to collect exudate aspirated from the wound; a pressure sensor configured to monitor a magnitude of pressure being generated by the pressure source, the magnitude increasing as a level of exudate in the canister increases; and a controller configured to: determine a pressure threshold at least from a level of activity of the pressure source, determine whether a subset of a first plurality of consecutive measurements of the magnitude satisfy the pressure threshold and whether a subset of a second plurality of consecutive measurements of the magnitude satisfy the pressure threshold, the first plurality of consecutive measurements comprising at least some of the same measurements as the second plurality of consecutive measurements, determine that the subset of the first plurality of consecutive measurements does not satisfy the pressure threshold and that the subset of the second plurality of consecutive measurements satisfies the pressure threshold, and indicate that the canister has reached a level of fluid responsive to the determination that the subset of the second plurality of consecutive measurements satisfies the pressure threshold.
 2. The wound therapy apparatus of claim 1, wherein the controller is configured to determine the pressure threshold further from a pressure setting for the pressure source.
 3. The wound therapy apparatus of claim 1, wherein the level of fluid is a canister full level.
 4. The wound therapy apparatus of claim 1, wherein the controller is configured to not indicate that the canister has reached the level of fluid in response to the determination that the subset of the first plurality of consecutive measurements does not satisfy the pressure threshold.
 5. The wound therapy apparatus of claim 1, wherein the pressure source comprises a vacuum pump, and the level of activity corresponds to a speed of the vacuum pump.
 6. The wound therapy apparatus of claim 5, further comprising a tachometer configured to measure the speed.
 7. The wound therapy apparatus of claim 1, wherein the first plurality of consecutive measurements comprises the same number of measurements as the second plurality of consecutive measurements, and the subset of the first plurality of consecutive measurements comprises the same number of measurements as the subset of the second plurality of consecutive measurements.
 8. The wound therapy apparatus of claim 1, wherein the first plurality of consecutive measurements are determined over a period of one minute.
 9. The wound therapy apparatus of claim 1, further comprising a display, the controller being configured to indicate with the display that the canister has reached the level of fluid.
 10. The wound therapy apparatus of claim 1, wherein the controller is configured to determine the pressure threshold further from a rate of a leak in the fluid flow path.
 11. The wound therapy apparatus of claim 1, wherein the controller is configured to suspend or terminate canister fluid level detection responsive to the level of activity indicating presence of a leak in the fluid flow path or presence of a low vacuum condition in the fluid flow path.
 12. The wound therapy apparatus of claim 1, wherein the pressure sensor is configured to monitor the magnitude at an inlet of the pressure source.
 13. A method of operating a wound therapy apparatus comprising a pressure source, a canister, and a controller, the method comprising: monitoring a magnitude of pressure being generated by the pressure source, the fluid flow path fluidically connecting the pressure source with a wound dressing and the canister, the magnitude increasing as a level of exudate in the canister increases; determining, by the controller, a pressure threshold from at least a level of activity of the pressure source; determining, by the controller, whether a subset of a first plurality of consecutive measurements of the magnitude satisfy the pressure threshold and whether a subset of a second plurality of consecutive measurements of the magnitude satisfy the pressure threshold, the first plurality of consecutive measurements comprising at least some of the same measurements as the second plurality of consecutive measurements; determining, by the controller, that the subset of the first plurality of consecutive measurements does not satisfy the pressure threshold and that the subset of the second plurality of consecutive measurements satisfies the pressure threshold; and indicating that the canister has reached a level of fluid responsive to determining that the subset of the second plurality of consecutive measurements satisfies the pressure threshold.
 14. The method of claim 13, wherein said determining the pressure threshold comprises determining the pressure threshold further from a pressure setting for the pressure source.
 15. The method of claim 13, wherein the level of fluid is a canister full level.
 16. The method of claim 13, further comprising, by the controller, not indicating that the canister has reached the level of fluid in response to determining that the subset of the first plurality of consecutive measurements does not satisfy the pressure threshold.
 17. The method of claim 13, further comprising determining the level of activity with a tachometer that measures a speed of the pressure source.
 18. The method of claim 13, wherein the first plurality of consecutive measurements comprises the same number of measurements as the second plurality of consecutive measurements, and the subset of the first plurality of consecutive measurements comprises the same number of measurements as the subset of the second plurality of consecutive measurements.
 19. The method of claim 13, further comprising suspending or terminating, by the controller, canister fluid level detection responsive to the level of activity indicating presence of a leak in the fluid flow path or presence of a low vacuum condition in the fluid flow path.
 20. The method of claim 13, wherein the pressure sensor monitors the magnitude at an inlet of the pressure source. 